(Adapted from the Applicant's Abstract) Persistent pulmonary hypertension of the newborn (PPHN) is characterized, in part by a structural remodeling of the vascular wall. This remodeling process involves vascular smooth muscle cell (SMC) replication and the synthesis of extracellular matrix components. Our understanding of the pathogenesis of persistent pulmonary hypertension of the newborn (PPHN) is dependent on a more complete knowledge of the molecular mechanisms underlying the control of SMC replication during development. The overall objective of our research program is to understand why SMC stop replicating following development. They believe that SMC acquires various growth suppressive mechanisms during their normal developmental maturation into quiescent, contractile cells, and their studies are designed to identify these mechanisms on a molecular level. Beginning with fully quiescent, adult tissues, they studied the molecular changes which occur as undifferentiated SMC "modulate" into more immature cells capable of replication, and identified developmentally acquired molecules endogenous to the mature blood vessel wall growth- essential transcription factor Oct-1, which is constitutive in cultured SMC, was repressed in vivo an in SMC cultured on artificial basement membranes. They determined that the heparan sulfate side chains of perlecan, the basement membrane proteoglycan, are the primary determinants of Oct-1 gene expression in SMC. These data are consistent with the demonstrated role for perlecan heperan sulfates in the inhibition Of SMC replication in vitro. Further, perlecan is expressed in vivo during vascular development in a pattern consistent with its potential role as an endogenous inhibitor of SMC replication. The major goals of this project are therefore to determine the mechanism of binding the SMC to perelcan/heperan sulfate matrices, to elucidate the intracellular signalling pathways activated by perlecan: SMC interactions, and to define, on a molecular level, the mechanism by which perlecan inhibits SMC replication and alters gene expression. They will also define the intracellular and extracellular factors which control perlecan gene expression in SMC through an analysis of the perlecan promotor region. Using in situ hybridizations, they will determine if the timed developmental pattern of perlecan gene expression is altered in experimental models of hyperoxia and hypoxia-induced neonatal hypertension. Finally, they will determine the effects of exogenous heparan-like molecules on hypoxia-and hyperoxia-induced SMC replication in vivo to assess their potential use as therapeutic agents for the treatment of PPHN. These studies should provide valuable information concerning the mechanisms underlying normal developmental growth suppression in the mature blood vessel wall. Elucidating the molecular basis for endogenous growth-inhibitory pathways may provide the basis for the future developmental of therapeutic agents capable of treating pulmonary of treating pulmonary and systematic vascular diseases involving abnormal SMC replication.